Development of UV-assisted ozone steam etching and investigation of its usability for SU-8 removal

We have developed ultraviolet (UV)-assisted ozone steam etching as a novel SU-8 removal technology. This technology is expected to remove SU-8 at a higher etch rate compared to a conventional wafer cleaning process based on ozone water immersion. An etching apparatus prototyped in this study achieves an etch rate greater than 100 nm min^-1 by intermittently rotating an SU-8-coated substrate on a spinner for spinning out the etching products under UV irradiation. Its complete removability is also verified by analyzing the surfaces of etched samples via scanning electron microscopy and x-ray photoelectron spectroscopy. In a micromolding process, the non-swelling removability is successfully demonstrated by removing a SU-8 sacrificial mold and leaving electroplated metal mushroom microstructures without destruction. Such a structure cannot be released by conventional resist strippers, because it is lifted up due to resist swelling. We believe this etching technology becomes a viable option to remove chemically-stable polymers such as SU-8 in microelectromechanical systems.